Effect of graphene nanoplatelets on the properties, pore structure and microstructure of cement composites

Graphene nanoplatelets (GNPs) with extraordinary mechanical properties have been extensively applied in various fields as reinforcing materials. However, the mechanism of the GNPs reinforcing effect on cement composites is still under debate. In this research, the GNPs were dispersed in mixing water by means of dispersant combining with ultrasonication. The GNPs cement composites with different GNPs contents were prepared and their mechanical performance were investigated. In addition, the effects of GNPs on the hydration products of cement-based materials were studied by using different analytical techniques. Meanwhile, the pore structure and microstructure of GNP/cement composites were observed with the help of Mercury intrusion porosimeter (MIP) and Scanning electron microscope (SEM/EDS). It is found that the addition of 0.05 wt% GNPs increase the compressive and flexural strengths by about 4.3%, 3.7% and 27.4%, 25.2% in 7 d and 28 d curing ages, respectively. The experimental results suggest that GNPs may contribute to promoting the crystalline of calcium hydroxide (CH) and the formation of silica tetrahedron in calcium silicate hydrate gels (C-S-H) at the early age. The cement composites exhibit a more compact and optimal pore structure through refining pore size and reducing total porosity. And GNPs can enhance cement composites in mechanisms of filling effect, pull-out effect, branching and deflection of cracks.